The invention relates to a method of manufacturing a thin-film magnetic field sensor comprising a substrate bearing an anisotropic thin film having an easy axis of magnetization.
West German Pat. No. 2,701,296 discloses a thin-film magnetic field sensor which is built up from a stack of thin-film on a substrate, namely, two structured metal layers which together form a coil; an anisotropic magnetic layer embedded in insulating layers is provided between the two metal layers. The inductivity of the coil is a function of the permeability of the magnetic layer. An external magnetic field is provided for orienting the magnetization of the magnetic layer along its easy axis. For producing the easy axis of magnetization which is essential for the function of the above mentioned sensor, the layer is manufactured by cathode sputtering on a substrate, and thus, during the deposition of the layer material, is exposed to a relatively strong d.c. magnetic field which lies in the plane of the substrate.
The magnetic layer then shows an easy axis of magnetization in the plane of the layer.
If a great number of seperate anisotropic magnetic layers has to be made, the known method is disadvantageous because neither the position of the substrates relative to the d.c. magnetic field nor the homogeneity of said field at the location of the magnetic layer formed can be adjusted accurately in a reproducible manner. During the deposition of the layer material on the substrates, magnetic stray fields are formed which are caused by the deposition of layer material occurring simultaneously in the immediate proximity of the substrate and partly also by the deposition apparatus itself. As a result, considerable fluctuations of the magnetic characteristics occur, which reduces the quality of the manufactured layers.
A further disadvantage of the conventional method is that it requires a particular deposition apparatus which enables the simultaneous action of a strong d.c. magnetic field. These apparatuses are not yet commercially available in a type which is suitable for batch fabrication.
Another disadvantage of the conventional method is that the deposition apparatuses have to be cleaned very often during continuous operation. This results in an expensive method of manufacturing magnetic layers having an easy axis of magnetization.